An analog circuit needs a voltage or a current as a reference of its operation. Therefore, generally, a reference signal generating circuit, such as a reference voltage generating circuit and a reference current generating circuit, is used. Particularly, an analog circuit that requires accuracy needs a reference signal generating circuit that is not dependent on fluctuations in power source or fluctuations in temperature.
For example, a reference current generating circuit is known as the reference signal generating circuit in which two current mirror circuits are connected in a loop shape and a current value is determined by one resistance.
[Patent Document 1] Japanese Laid-open Patent Publication No. 7-146725
With a decrease in power source voltage of a semiconductor device, a reference signal generating circuit that operates at a further low voltage is needed. In addition, when a reference signal generating circuit is packaged in a chip, it is necessary not to be dependent on fluctuations in power source or fluctuations in temperature as much as possible.